This invention relates to tabs for disposable diapers, geriatric briefs, surgical drapes or other articles requiring a fastener tab and to tapes convertible to make such tabs.
In the manufacture of disposable diapers, it is typical practice for the diaper manufacturer to provide diaper fastener tabs fixed to the diaper proper. Each tab is permanently attached at one end thereof to the diaper shell at a "factory joint" at the rear of the diaper. The other end of the tab is arranged for fastening and refastening the diaper closed to a reinforcing tape or landing zone at a "user joint" at the front of the diaper. To that end, the tab includes a polymeric substrate or backing film and an adhesive layer.
It is desirable to provide such tabs with an increased softness. Such softness may be provided for aesthetic and/or functional purposes as discussed more fully below.
Tactile softness may be desirable solely for aesthetic purposes as well as for infant comfort. Pliant softness characterized by highly flexible or conformable film deformation properties provides infant comfort by reducing the tendency to chafe or irritate the infant's skin upon contact. To some extent, both tactile and pliant film softness may combine to reduce chafing and irritation.
Heretofore, tactile and/or pliant film softness have been provided by formulation of the polymeric film with polymers of relatively lower modulus. For example, polyethylene homopolymers may be used to provide a relatively soft feeling and highly flexible tab substrate or backing film. Similarly, polyethylene may be combined as a copolymer or physically blended with other polymers such as polypropylene to increase the softness of the resulting copolymer or polymer blend. Other polymers, such as ethylene-vinyl acetate (EVA) may also be used as copolymer or blended constituents.
The use of polyethylene homopolymers, copolymers or blends to achieve tab softness is not entirely satisfactory since polyethylene tends to cause adhesive aging problems characterized by accelerated rates of decrease of adhesion strength with age. The aging problems are believed to be associated with the tendency of one or more adhesive components to migrate into the polyethylene moiety (polyethylene copolymer or blended material) with swelling of the latter. In the case of polypropylene blends and copolymers with polyethylene, it is believed that no more than about five percent polyethylene by weight may be present in order to avoid unacceptable adhesive aging characteristics.
As compared with films of polypropylene homopolymer, polyethylene copolymers and physical blends tend to be characterized by lower modulus values. Therefore, it is expected that tab substrate or backing films of such polyethylene materials will require slightly higher thicknesses than the 4.2 to 6 mil thicknesses used for polypropylene in order to assure film stability and ease of handling during machine processing. Of course, such polyethylene, polypropylene and/or copolymers thereof at higher thicknesses also tend to result in a cost disadvantage due to the additional material costs and the higher costs of copolymer films as compared with homopolymer films.
The outer side of polymeric fastener tabs have been embossed to provide them with a roughened outer surface. Various embossing patterns have resulted in corresponding degrees of roughness. One convenient measure of surface roughness is provided by the "Ra" roughness average or value measured in angstroms with a Dektak 3030 profile measuring system using a 2.5 um radius stylus. (The Dektak 3030 profile measuring system is manufactured by the Sloan Technology subsidiary of Veeco Instruments Inc. of Santa Barbara, Calif.) The Ra roughness average or value of a surface is defined as the distance between the average peak or projection height and an imaginary median line on the sample surface positioned so that the areas enclosed by the peak portions above the line will be equal to the areas enclosed by the valleys between the peak portions below the line. Hereinafter, such Ra roughness averages or values are reported to indicate the relative roughnesses of surface morphologies.
Prior art diaper fastener tabs have been found to range in roughness from Ra values of 25,000 angstroms to 170,000 angstroms due to various finish processing techniques including embossing. Presumably such roughness is used to avoid the gloss finish otherwise obtained by finish rolling plastic film with a polished steel roll.
It is known from U.S. Pat. No. 5,147,347 to emboss or otherwise texture the outer surface of a diaper shell to provide a non-glossy, matte finish material which the patentee indicates is soft to the touch, provides a more garment-like appearance, and produces less rattling noise when manipulated. It is believed that such diaper shell roughening tends to cause poor adhesive contact efficiency which is associated with the inadvertent "pop-off" release of diaper tabs and/or tears of the diaper shell at the factory joint. The contact efficiency is reduced by surface morphologies of relatively rough characteristics having significant variations in surface projections and/or relief dimensions. In some instances, the contact efficiency is further decreased by roughening of the fastener tab adhesive layer during processing. More particularly, fastener tabs are typically formed of self-wound tapes and the adhesive layer of the wound tape replicates the roughness or embossing pattern of the substrate. The exposed surface of the adhesive layer of the tab is thereby roughened and itself may further inhibit adhesive contact efficiency.